JP4397870B2 - Image projection system using a DC high-pressure discharge lamp - Google Patents

Description

  The present invention relates to an image projection system equipped with an optical element and a color filter.

  The image projection system irradiates light to a color filter that rotates at high speed, and extracts, for example, three primary colors (ie, R (red), G (green), and B (blue)) in a time-sharing manner. This is a system that creates an image pattern using a reflective optical element called (registered trademark) and projects a color image on a screen via a projection lens system, and is used in home theaters and RPTVs (rear projection televisions). ing.

  High-pressure discharge lamps used as light sources for image projection systems are classified into two types depending on the drive current waveform: a method of lighting with a rectangular alternating current (AC method) and a method of lighting with a direct current (DC method). The In the initial system, the AC system is the mainstream, and the color filter is generally a simple one composed only of the three primary colors of R, G, and B.

  It is important to change the color tone of the projected color image according to the user's preference. In this regard, for example, in Patent Document 1, in an image projection system including a color filter composed of three types of color segments, R, G, and B, a light source is selected according to a specific color (R, G, B). An image projection apparatus is disclosed in which the color tone can be freely changed by changing the output power used for driving (however, the embodiments are all based on an AC light source).

  Thus, in an image projection system including a digital optical element such as DMD (registered trademark), controlling the magnitude of the driving current of the high-pressure discharge lamp while synchronizing with a specific color segment is highly reproducible. It is attracting attention as one of the technologies that can provide rich expressive power, such as adjusting the color tone or expressing a bright red color according to the user's preference.

Japanese National Patent Publication No. 8-505031

  By the way, the electrode part of the high-pressure discharge lamp has a cathode (cathode) that emits electrons and an anode (anode) that receives electrons emitted from the cathode. Since the electron accelerated by the electric field collides with the anode, it is heated to a high temperature and consumed by evaporation. Since the polarity of the alternating current type high pressure discharge lamp changes at a constant cycle, the cathode and the anode are periodically switched. As a result, both electrodes are consumed.

  FIG. 4A shows the state of electrode structures 101a and 101b and arc discharge A100 of a general AC high pressure discharge lamp. As shown in this figure, in the case of the AC method, the two electrodes are designed to have the same shape and size so that the electrodes are evenly consumed. The direction of the AC lamp current is switched between a positive half cycle and a negative half cycle. For example, if the direction of the current in the positive half cycle is the arrow C1, the cathode (cathode) in the meantime is 101a and the anode (anode) is 101b. At this time, the bright spot of the arc is generated in the vicinity of the cathode and thus appears around K101. On the other hand, the direction of the current in the negative half cycle is the arrow C2, this time the cathode is 101b, the anode is 101a, and the bright spot of the arc appears around K102.

  In order not to deteriorate the life characteristics of the AC type high pressure discharge lamp so that the consumption of the electrode part is made as uniform as possible, the average power supplied to the light source can be adjusted to be equal to plus and minus. is necessary. However, it is difficult to maintain the symmetry of the current waveform when the input current waveform to the high pressure discharge lamp is manipulated by changing the magnitude of the drive current in segment units in order to obtain rich expressive power.

  For example, FIG. 4B shows an image projection apparatus of an AC system in which “a red pulse amplitude (both positive and negative pulses) is larger than a blue pulse amplitude, and a blue pulse amplitude is a green pulse. In this example, the drive current of the light source is changed so as to be larger than the amplitude of the light source (see FIG. 2b of the above-mentioned Patent Document 1). The color segment and the drive current must be properly synchronized, which is extremely difficult to implement. Note that the “detailed description of the invention” of Patent Document 1 only describes “It is necessary to operate so that the power of the positive pulse is equal to the power of the negative pulse.” How to take is not clear.

  Furthermore, in the AC method, the direction of electron emission between the electrodes in the high-pressure discharge lamp is switched between a positive half cycle and a negative half cycle, so that the arc discharge luminescent spot (light emission position) is a positive half cycle and a negative half cycle. Move slightly with the cycle. For this reason, the amount of light input to the digital optical element fluctuates slightly, resulting in a disturbed gradation.

  As described above, it is difficult to synchronize the color segment with the drive current if the drive current is changed in the segment unit for the AC type high pressure discharge lamp. In addition, the AC type high-pressure discharge lamp has an inherent problem inherent in the AC type in which the bright spot position fluctuates periodically.

  The present invention has been made in view of the above, and adopts a novel synchronization method that can reliably synchronize the driving current of the high-pressure discharge lamp and the color segment even if the magnitude of the driving current is changed in units of segments. The main purpose is to provide an image projection system.

The image projection system according to the present invention includes a direct-current high-pressure discharge lamp 1, a rotary color filter 3 that separates a light beam Φ1 emitted from the high-pressure discharge lamp into a plurality of colors, and a light beam Φ2 that has passed through the color filter. A reflection type optical element 4 for gradation and modulation by a video signal, direct current lighting means 5 for driving the high pressure discharge lamp with a direct current, and a light flux Φ3 reflected by the optical element is projected on a screen. An image projection system including a projection lens system 6 for detecting the rotation of the color filter and generating a synchronization signal S by detecting the rotation of the color filter, wherein the synchronization signal generator 9 rotates the color filter. given that a plurality of on-off pattern synchronized, which both generates the synchronizing signal S of different rectangular pulses on time, a one-to-one correspondence with the pulse width Different power levels (e.g., L1 to L4), and a timing after the elapse of predetermined time (T0) from the detection of the pulse defined by the on time of the synchronization signal (S), detected pulse width The power level is set based on the detected pulse width by outputting to the high-pressure discharge lamp until the predetermined time (T0) elapses from the detection of the next pulse .

  As described above, in the present invention, the on / off pattern of the synchronization signal S (specifically, the rectangular pulses Ts1 to Ts4 having different on times) and the power levels (L1 to L4) output to the high pressure discharge lamp are in a one-to-one relationship. It is set in advance so as to correspond, and at the timing of the next color segment that receives the synchronization signal S of a predetermined pattern, the corresponding power level (L1 for Ts1) is output to the high pressure discharge lamp. If the output timing is set after a predetermined time T0 has elapsed with reference to the rising time of the synchronizing signal, the rotation of the color filter (that is, the color segment) and the synchronizing signal can be accurately synchronized.

  In this system, it is preferable that the maximum value L4 of the power level is set to 1.1 times or more of the minimum value L1 of the power level in terms of suppressing flicker caused by arc jump.

  In the present system, the electrode of the high pressure discharge lamp is preferably configured such that the anode (anode) has a larger mass than the cathode (cathode). As the maximum power level (L4) is increased, the anode is more likely to be consumed (evaporation due to heating). By increasing the mass of the anode in advance, the maximum power level (L4) and minimum value are increased. This is because even if the ratio of (L1) is increased, the life of the high-pressure discharge lamp can be made difficult to deteriorate.

According to the present invention, it is possible to accurately synchronize with different supply power of the high-pressure discharge lamp supplied to each color segment. Further, different power levels can be freely supplied to the color segments of the video field, and flicker can be suppressed and a stable arc can be maintained. Further, in the present invention, various shades can be expressed only by changing the pattern of the synchronization signal, and it is not necessary to change the circuit of the lighting means, so that the degree of freedom in system design is extremely high.

(First embodiment)
-System configuration-
FIG. 1 shows an example of a block diagram illustrating the system configuration of an image projection system according to the present invention. This system includes a light source E composed of a DC high pressure discharge lamp 1 and a reflector 2, a color filter 3 including a plurality of color segments 3a to 3f, an optical element 4, and a projection lens system 6. . The light flux Φ emitted from the high-pressure discharge lamp 1 is reflected directly or reflected by the reflector 2, and the color filter 3 is irradiated with the light flux Φ 1 and is optically modulated by the optical element 4, and then a predetermined image pattern is projected onto the projection lens system 6. Through the screen 7.

  The color filter 3 includes a plurality of color segments made of a dichroic filter having a property of selectively passing visible light wavelengths. The color filter 3 in FIG. 1 includes six colors (3a to 3f) of R, G, B, Y, M, and C (red, green, blue, yellow, magenta, and cyan).

  The optical element 4 is formed of a reflective digital light modulation element such as DMD (registered trademark), reflects the light flux Φ2 that has passed through the color segments 3a to 3f and separated into the respective colors, and is received from the optical element driving device 14. It is a device for performing optical modulation by a supplied video signal (for example, a video signal).

  The DMD (registered trademark) is an optical element (light modulation element) for giving gradation to the light of each segment that has passed through the color filter, and for performing gradation with the video signal and modulating the video signal. For example, a large number of mirror elements are mounted on a semiconductor memory cell. The inclination of each mirror element is controlled by the optical element driving device 14, and a predetermined pattern can be created by switching between passage and blocking of light in each mirror element.

  The DC lighting means 5 includes a DC power supply circuit and a control circuit that selectively outputs a plurality of power levels according to a synchronization signal, and supplies a lamp current for lighting the high-pressure discharge lamp 1. Details of the drive current pattern to the high pressure discharge lamp will be described later.

  The projection lens system 6 is an optical lens for projecting the light beam Φ3 reflected by the surface of the optical element 4 onto the screen (7).

  The color filter driving device 8 is a driving device for rotating the color filter 3 and functions to rotate the color filter 3 at a constant speed. For example, in the case of a video signal having a frequency of 60 Hz for one frame (one screen changes 60 times per second), the color filter rotates at a speed that is an integral multiple of the frequency of the one frame (for example, twice, that is, a frequency of 120 Hz). .

  The light beam Φ1 irradiated from the light source E is color-separated in a time division manner when passing through the segments 3a to 3f of the color filter 3 rotating at a constant speed. The luminous flux Φ2 separated into the respective colors enters the optical element (4) through a light pipe (not shown) or the like.

  The color filter 3 is provided with a position index 3g for detecting timing. For example, when the photosensor detects the position index 3g, the timing of one rotation of the color filter is detected and the timing reference signal S0 is generated. The reference signal S0 is input to the synchronization signal generator 9, and a plurality of synchronization signals synchronized with each color segment are input to the DC lighting means 5 with the reference signal S0 as a reference.

-Current drive pattern-
FIG. 2 shows the state of the color filter segment (upper stage), the DC lamp current waveform I _L (second stage), the waveform of the synchronization signal S (third stage), and the irradiation from the high-pressure discharge lamp 1 in the image projection system according to the present invention. The signal intensity of the emitted light beam Φ1 is illustrated on the same time axis. Here, a color filter including six segments of R, G, B, Y, M, and C (red, green, blue, yellow, magenta, and cyan) as shown in FIG. An example (one frame 60 Hz, video field 120 Hz) rotated at double speed is shown. In practice, the spoke time may be set to absorb the influence of the boundary of the color segment, but the description of the transient characteristics is omitted.

Power level shows an example of setting four kinds of L1, L2, L3, L4 in ascending order, short turn Ts1 of each on-time of the synchronization signal S, Ts2, Ts3, identified by Ts4. The current intensity of any one of the plurality of power levels set in advance is output after a predetermined time T0 has elapsed with reference to the rising time of the synchronization signal.

That is, set the next drive current I _L when it detects a pulse width of Ts1 to level L1, set the next drive current I _L when it detects a pulse width of Ts2 to the level of L2, Ts3 pulse width the set the following drive current I _L when detecting the level of L3, when it detects a pulse width of Ts4 is to set the next drive current I _L to the level of L4.

  For example, Ts1 = 100 μs, Ts2 = 150 μs, Ts3 = 200 μs, Ts4 = 250 μs, and T0 = 300 μs are set, and L1, L2, L3, and L4 are set in advance corresponding thereto. In addition, even if 4 times speed is considered in 6 color segments, it is about 690 μs per segment (= 1/60 Hz / 4 times / 6 segments). Since the magnitude of T0 (= 300 μs) is smaller than this value, all of the above set values are appropriate set values.

  In order to finely adjust the error of the color segment, it is only necessary to adjust this timing by the control circuit in the synchronizing signal generator 9, and the DC lighting means 5 does not need to be changed. Even if the angle of each color segment is changed, the frame frequency is changed to 50 Hz, for example, or the rotation speed of the color filter is changed, only the timing of the synchronization signal need be changed.

For example, in the example of the DC lamp current waveform (second stage) in FIG.
L1 green (G)
L2 ... Blue (B), Magenta (M)
L3 ... Yellow (Y), Cyan (C)
L4 ... Red (R)
Is associated.

With this setting, an image with a slightly lower color temperature can be obtained as a whole. Conversely, for example, as shown in the DC lamp current waveform (first stage) in FIG. 2B, B (blue) and R (red) are interchanged,
L1 green (G)
L2 ... Red (R), Magenta (M)
L3 ... Yellow (Y), Cyan (C)
L4 ... Blue (B)
As a result, an image with a slightly higher color temperature can be obtained as a whole.

  In this case, all that is necessary is to change the synchronization signal S as shown in the lower part of FIG. 2B and replace the pattern of the synchronization signal for selecting the power levels of R (red) and B (blue). It is.

  As described above, according to the image projection system of the present invention, it is possible to express various colors according to the user's preference simply by changing the pattern of the synchronization signal. Moreover, since it is not necessary to change the circuit of the lighting means, the degree of freedom in system design is extremely high.

  In the image projection system according to the present invention, since the high-pressure discharge lamp serving as the light source is based on the direct current method, there is no need to consider polarity switching as in the alternating current method, and after receiving the synchronization signal according to the type of the synchronization signal. It is easy to generate the current waveform as described above in the segments. By the way, in the case of the AC system, the limitation is large because symmetry and the like must be taken into consideration, but this system has an advantage that the power levels (L1 to L4) can be freely arranged.

  In the above embodiment, the number of color segments is six (RGBYMC) and the number of power levels is four stages (L1 to L4). However, these are only examples, and the correspondence relationship between the synchronization signal and the power level is shown. It goes without saying that the number of segments and the number of power levels can be freely changed if changed.

  In this system, since the high-pressure discharge lamp is driven by a direct current system, the bright point of the arc is fixed in one direction on the cathode side, so that the gradation is hardly disturbed. It is known that arc jump can be suppressed by superimposing a pulse current on a direct current (for example, Japanese Patent Application Laid-Open No. 2004-212890), but the drive current waveform of this system has a pulse of the same polarity as the direct current. Since it is equivalent to the superimposed one, if a power level difference (L1 to L4) of a certain level or more is added in the video field, an effect of suppressing flicker caused by arc jump is also expected. According to experiments, the flicker suppression effect was confirmed when the difference between the maximum value (L4) and the minimum value (L1) of the power level was 1.1 times or more in the ratio of the maximum value / minimum value.

(Second Embodiment)
FIG. 3 shows a state of electrode structures 1a and 1b and arc discharge A of a general DC type high pressure discharge lamp. As shown in this figure, the DC-type high-pressure discharge lamp shown in this embodiment is configured such that the mass of the anode (anode) 1b is larger than that of the cathode (cathode) 1a. Usually, this type of DC-type high-pressure discharge lamp has an anode mass / cathode mass of typically about 1.5 to 2. The current flows in the direction of arrow R in the figure, and arc discharge A as shown in the figure occurs. At this time, the bright spot K appears in the vicinity of the cathode 1b.

  In the experiment, when the mass ratio of the anode and the cathode was set to about 2.5 (2.3 to 2.7), which was slightly higher than usual, the maximum value (L4) of the power level was 150% of the minimum value (L1). (1.5 times) could be set. This means that the range of color tones that can be adjusted is large. If the level difference is further increased, the anode side is heated intensely and the tungsten electrode evaporates, which may shorten the life of the discharge lamp. However, if the vapor pressure and electrode shape of the discharge lamp are optimized, the level difference can be set slightly larger.

  In the case of the alternating current method, both electrodes alternately become anodes and cathodes, so that electrodes having an appropriately large mass are necessary in order not to deteriorate the life characteristics with respect to the maximum power level (L4). It is thought that it is. However, in that case, the arc tends to become unstable because the temperature of the electrode is excessively lowered during the period of operation as the cathode. Thus, in the case of the alternating current method, the electrodes are required to have contradictory characteristics, so that the power level difference cannot be increased. Therefore, it can be said that making the electrodes asymmetric as in this embodiment has a great effect only when applied to a direct current system like the present system.

  The image projection system according to the present invention can freely supply different power levels to the color segments of the video field, suppress flicker caused by arc jump, and maintain the arc stably. In particular, when the mass of the anode is made larger than that of the cathode, the level difference between the maximum value and the minimum value of the power level can be set to, for example, about 150%, so that the range of color tones that can be changed according to user preferences is large. In addition, since the bright spot position does not vary because of the direct current method, no error occurs in the light beam (Φ) that irradiates the color filter for each video field, and a stable light beam can be continuously output.

Block diagram of the present invention The figure which shows the relationship between the lamp current waveform of this invention, and a synchronizing signal The figure which shows the electrode structure of the high pressure discharge lamp of this invention FIG. 5A is a diagram showing an electrode structure of a conventional AC type high pressure discharge lamp. FIG. 5B is a diagram showing an example of a drive current waveform of a conventional AC type image projection apparatus.

Explanation of symbols

_IL DC lamp current E Light source S Synchronization signal Φ Light (light beam)
DESCRIPTION OF SYMBOLS 1 High pressure discharge lamp 2 Reflector 3 Color filter 3a-3f Color segment 3g Position index 4 Optical element 5 DC lighting means 6 Projection lens system 7 Screen 8 Color filter drive device 9 Synchronization signal generator 13 Video input part 14 Optical element drive element

Claims (3)

A direct current type high pressure discharge lamp (1), a rotary color filter (3) that separates a light beam (Φ1) emitted from the high pressure discharge lamp into a plurality of colors, and a light beam (Φ2) that has passed through the color filter. Reflective optical element (4) for gradation and modulation by a video signal, DC lighting means (5) for driving the high-pressure discharge lamp with a direct current, and light flux (Φ3) reflected by the optical element An image projection system including a projection lens system (6) for projecting the image on a screen and a synchronization signal generator (9) for detecting the rotation of the color filter and generating a synchronization signal (S),
The synchronization signal generator (9) generates a synchronization signal (S) having a plurality of on-off patterns synchronized with the rotation of the color filter and having rectangular pulses having different on-times, and has a one-to-one correspondence with the pulse width. to a plurality of power levels differ corresponding to a timing after the elapse of predetermined time (T0) from the detection of the pulse defined by the on time of the synchronization signal (S), the next pulse of the detected pulse width The power level is set based on the detected pulse width by outputting to the high-pressure discharge lamp until the predetermined time (T0) elapses from the detection of. The image projection system according to claim 1, wherein the maximum value of the power level is set to 1.1 times or more of the minimum value of the power level. The image projection system according to claim 1, wherein an electrode of the high-pressure discharge lamp is configured such that an anode has a larger mass than a cathode.

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